Many hearing disorders are based upon abnormal states of the external, middle or inner ear. Quantitative data can be obtained by utilizing acoustic signals and responses measured in the ear canal. This data can be combined with other measurements to provide information used in the detection and diagnosis of hearing disorders, and the clinical management of existing hearing disorders.
One of the most basic acoustic tests has to do with the characterization of the linear response of the ear, assessed by measurements of the impedance, reflectance, reflectometry, impulse response and/or reflection function. The standard clinical impedance test is based upon tympanometry, which measures the acoustic impedance at a single frequency, or at a discrete range of frequencies. Tympanometry was developed for use in adults, and it is widely held that it is grossly inaccurate in testing neonates. One of the contributing factors is that tympanometry is dependent upon static pressurization of the ear canal, and this static pressure produces artifacts that are particularly troublesome in infants. Nonetheless, the clinical importance of measuring the linear response of the ear is well documented.
It is well known that the human ear reflects sound pressure at very long latencies, 5-20 ms, after the presentation of an acoustic stimulus in the ear canal. However, it is unknown to what extent these so-called evoked otoacoustic emissions (EOAE) represent a delayed reflection of the acoustic energy in the original stimulus (i.e., a passive model) or represent energy output from sites of power generation within the inner ear (i.e., an active-source model).
At present there is no convenient technique available to measure the linear and nonlinear responses of the ear and to diagnose clinical abnormalities in the ear. Therefore, it can be appreciated that there is a significant need for an instrument to characterize the linear and nonlinear responses of the ear. This and other advantages of the present invention will be apparent from the following detailed description taken in conjunction with the Figures.